Figure 2.

The immunocompetence of honeybees at different developmental stages to Escherichia coli infection. The immunocompetence of honeybees to Escherichia coli (E. coli) infection varies among different development stages. Honeybees go through the larval stage and then the pupal stage before becoming adult. High-dose injection of E. coli into honeybee larvae causes a humoral immunity response and then induces the synthesis of antimicrobial peptides (AMPs), including defensin1, abaecin and hymenoptaecin, which can repress the multiplication of E. coli, and the larvae can survive. Pupae are completely incapable of activating cellular and humoral immune reactions upon E. coli infection, resulting in the rapid proliferation of E. coli, ultimately triggering the death of pupae. Moreover, both the humoral and cellular immune responses play important roles when adult honeybees are infected with E. coli. Prophenoloxidase is activated, resulting in synthesis of melanin and quinones. In the humoral immune response, AMPs, phenoloxidase (PO), carboxylesterases (CEs), peptidoglycan recognition proteins (PGRPs) and immune responsive protein 30 (IRP30) are detected, and in the cellular immune response, nodules are formed. All of these immune reactions can repress the amplification of E. coli, resulting in the survival of adults.